When we are talking about a "sequence of actions" it is correct to use the simple past. I would like to know if it is possible to use past perfect with the verb "spend" because first she spent 800 pounds before getting to Costa Rica- The key of the book says that the simple past is the only alternative but I don't agree.
Here is the text: Samantha... (spend)800 pounds of her own money getting to Costa Rica. First, she... (fly) to Miami. Then she... (catch) a plane to San José.

Samantha spent 800 pounds of her own money getting to Costa Rica. First, she flew to Miami. Then she caught a plane to San Jose.

Past perfect of "spend" would not make sense in that example. Past perfect is what happened first: "she flew to Miami." She didn't "spend" first. The "spend" sentence is the conclusion, what resulted at the end.

Samantha spent 800 pounds of her own money getting to Costa Rica. First, she had flown to Miami. Then she caught a plane to San Jose.

By the time she got to Costa Rica she had spent 800 pounds (first she spent 800 pounds and then she got to Costa Rica. I don't agree with your answer. Thanks anyway